Emission control devices, such as a three-way catalyst, coupled to the exhaust of a combustion engine reduce combustion by-products such as carbon monoxide, hydrocarbons, and oxides of nitrogen. To reduce emissions, catalyst monitoring methods are used to detect when an emission control device has reached its threshold use and is to be replaced. Reliable catalyst monitoring may reduce costs by decreasing erroneous characterization of useful catalyst as expended catalyst, or may reduce emissions by decreasing erroneous characterization of degraded catalyst as useful catalyst.
Various approaches for catalyst monitoring have been developed including methods provided for monitoring an emission control device comprising following a deceleration fuel shut-off duration, indicating degradation of the emission control device based on an integrated air-fuel and steady-state based index ratio diagnostic method. Support vector machine algorithms have further been applied to catalyst monitoring systems for classifying integrated air-fuel parameters to provide the degradation indication.
The inventors herein have recognized issues with the above approaches. Namely, the index ratio method has been proven to work only with partial volume systems. Furthermore, existing integrated air-fuel methods do not perform well in vehicles such as a limousine, in which an after-treatment system may be located farther away from a universal exhaust gas oxygen upstream sensor as compared to that in a more regularly sized vehicle. Thus, the capability and robustness of traditional catalyst monitoring methods may be reduced owing to large transport delays between the upstream universal exhaust-gas oxygen sensor and the air-fuel sensor downstream from the catalyst. Further still, support vector machine algorithms may use large amounts of memory, arising from a number of support vectors needed to define the classification plane.
One approach that at least partially addresses the above issues comprises a method of monitoring catalyst performance comprising computing a total fuel mass following a deceleration fuel shut-off event until a heated exhaust gas oxygen sensor switch. In particular, the method may include computing a transport delay to account for vehicles in which the after-treatment system is located farther away from an upstream exhaust gas oxygen sensor. Furthermore, catalyst degradation may be indicated based on the total fuel mass by applying a set of parameter readings to a support vector machine, wherein the support vector machine may employ clustering algorithms and/or a buffer region to reduce the number of support vectors. By computing a total fuel mass, the catalyst monitoring method can be made robust for both partial and full volume systems. In this manner, a catalyst monitoring method is described, providing increased robustness for partial and full volume systems and those with large transport delays, and having reduced memory usage as compared with traditional catalyst monitoring methods.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.